Smelting volatilizable metals



Feb. 16 1926.

Crude SMELTING VOLATILIZABLE METALS 2/7612 COCla W. A. OGG- Filed May 25, 1925 ZnO Zn Cl: CdCLa lnwemior: 1

Patented Feb. 16, 1926.

UNITED. STATES,

WILLIAM OGG, OF NEWTON, MASSACHUQETTS.

SMELTIKG VOIIATILIZABLE METALS.

Application men ma 25, 1925. I Serial No. 82,563.

To all whom it may concern Be it known that 1, WILLIAM A. Dec, a citizen of the United States, and a resident of Newton, county of Middlesex, and State of Massachusetts, have invented an Improvement in Smelting Volatilizable Metals, of which the following description, in connection with the accompanying drawings, is a specification, like characters on the drawings representing like parts.

This inventirm relates to the smelting of material bearing volatilizable metals particularly, but not exclusively, concentrated ores of zinc and has for its object the provision of an eflicient and more economical method of smelting as practiced with retorts and condensers. The invention is advantageously but not necessarily practiced in connection with the process more fully described inmy prior'application, Serial No.

7561, filed Feb. 7, 1925.

My invention will be readily understood by reference to the followin description thereof, more particularly w en taken in 5 connection with the accompanying drawin illustrating diagrammatically a preferre process exemplifying the invention.

' Before proceeding to the description of the process as, such, it will be convenient to refer briefly to the furnace commonly used for the reduction of. zinc ores or ores of like volatilizable metals. Such a furnace yincludes tiers of cylindrical retorts as indicated in the diagram b the showing of one .such retort at 3, t ese retorts being commonly made of fire clay'or other suitablerefractory material and being'removably supported inthe combustion chamberof the furnace. Thezbrs-{whichmay be 40 metallic oxidesj-or sulphides converted to oxides by 'roasting, are mixed withthe reduction fuel, usually-"coal or coke free as far as possible from sulphur, and the mixturechargedinto theretort. In practice, when smelting zinc bearing ores the retorts aresubjected to a temperature of about 1300 C. by externally applied heat which reduces the ore and being above the boilin point of zinc volatilizesthe metal, whic passes out of the retort as a vapor and is condensed toa liquid in a condenser 5,,

"the latter consisting of a short frusto-coniof the condenser an cal continuation of the retort projecting from the reduction chamber and being commonly detachably connected with the retort.

In conducting the smelting operation it has been common practice to add common salt, sodium chloride, to the charge, for example, a weight of salt "equal to about 2% of the weight of the-roasted ore. The exact functions of the salt are not exactly understood but it is believed, first, that it acts as a binder on the charge, which is desirable from the operating standpoint; second, that it acts as a flux to make the droplets of zinc in the condenser coalesce; third, that it acts to remove the coating of zinc oxide fromthe so-called blue powder; and fourth, that it materially reduces the amount of blue powder produced which would require re -smelting.

The introduction of chlorine into the charge by the use of salt produces, of course,

a certain amount of zinc chloride which,

being volatilizable, is discharged from the retort. In accordance with'my present in vention I permit a substantial proportion of the vapors to pass from the mouth of the condenser and collect the ,metal values in these escaping vapors by deposit. Thus, in the diagram I have shown the end of the condenser 5 as entering a hood 7 in which 7 the vapors are preferably burned in a large excess of air to produce a fume .product" consisting largely of zinc oxide which may be led to a bag house or similar settling chamber, illustrated diagrammatically by the bag 9, wherein the metal values are recovered in the form of a powder or fume. As contrasted with prior'processes in which the escape of vapors from the condenser was kept as low as. possible and represented a loss, I propose deliberately to operate the furnace so that a substantial fraction of themetal values are assed from the mouth collected as a fume product. On account of the volatility of the zinc chloride it will be substantially entirely carried over in the fume product.

Zinc ores also may frequently contain a certain proportion-of cadmium and a considerable portion of this metal will be selectively converted to chloride'and be carried over into the fume product. Thus, for

' was present as chloride.

The step of the process just described may preferably be practiced in the manner described in my prior application referred 'to. Prior to the invention therein described good practice in smelting ZlIlC ore was substantially as follows. The retort was loaded with mixed ore and fuel to roughly of its cubical capacity. The recovery of metal content was about Sil in the form of spelter and of the remainder about 7.75% was in the residue. About 1% was absorbed by the walls of the retort and the condenser and the remaining loss of 1.7 5%was principally in the form of escaping vapors from the mouth of the condenser which it was uneconomical' to attempt to recover. In

accordance with my invention as described in the said application, in order to permit more ore to be treated at one time and to increase the percentage of recovery "of metal values minimizing" the expense per unit of commercially available metal pro duced, the. retort is deliberately substantially overcharged beyond the capacity ofthe condenser to condense efliciently and preferably to its full cubical capacity.

Sufiicient heat is applied to the retorts sub-,

stantially to reduce all the metal in oxidized form and the condenser is operated at full condensing capacity for the given operating conditions to provide a large recovery of spelter while at the same time by the deliberate overcharge a substantial fraction of the metal values is intentionally caused to escape from the condenser to be recovered by deposit as a fume product.

By utilizing salt in an increased charge of this nature a large recovery of spelter may be provided for with the advantageous functions ofsalt as utilized in the prior art and the chloridewill be collected substantially entirely in the fume product, as will also part of the cadmium value if present.

The presence of chloride in zinc oxide fume is undesirable since zinc, chloride is a soluble salt. If only small uantities of chloride were present it woul possible to eliminate them by re-heating butif salt is used and large amounts of metal chloride recovered in the fume as above .described, re-heating is not a satisfactory method of purifying-the fume. I therefore arrange the separation of the chlorine values from the fumeproduct preferably in such manner as to'permit their return to the furnace together witlia fresh supply of the roasted zinc ore, or other crude zinccreasing the amount of may be charged into aretort of given bearing material, and reduction fuel to provide a charge for a subsequent volatilizing o eration, thus economizing in the use of sa t or other fluxing reagent which after the first mix need be added only to make up for operating losses. Furthermore, when the chloride is thus returned to the furnace there is no substantial buildin thewash water and an insoluble residue remaining consisting of a very ure zinc oxide unchanged as to the size 0 particles and which needs only to be dried and disintegrated to restore it to itscondition of a very fine zinc' oxide free of chloride and other soluble salts and substantially free of leadand cadmium. If the quantity of cadmium in the original ore were substantial, the cadmium may be recovered from the Wash water by decanting this wash water to a precipitating tank and adding metallic zinc thereto which will precipitate the cadmium as metal in sponge form, leaving the solution substantially one of .pure zinc chloride. This zinc chloride solution may then be treated with a suitable r nt to precipitate the zinc values there rom and it will be convenient to use an oxide for this purpose, prefcrabl lime, that is, calcium oxide. By the a dition of lime zinc hydroxide is precipitated which may readily be converted to the oxide for utilization as such or as a raw material for the production of a high grade of spelter. The calcium-chloride solution may then be mixed with ,further crude zinc-bearing material and reduction fuel to form a of the salt. -The" fact that the calcium' chloride is recovered in a water solution is not a disadvantage since it is customary and advantageous" to "wet down the charge of the furnace with water. The calcium chloride solution takes the water as well as of the salt. I

The calcium chloride solution is also suitable for; use as a bindingagent and for this reason may be utilized in connection with reduction fuel and crude zincbearing material for the production of briquets, the briquettin of the charge inmetal values that capacity.

have described indetail one particular place of the series of operations exemplifying the method of my invention. Obviously these may be widely varied, substituted for by others, added to and in part omitted without departing from the principles of the invention.

What I claim and desire to secure by Letters Patent I shall express in the following claims.

1. A method of recovering metal values from crude zinc-bearing material which comprises volatilizing the metal content of such material .in the presence of chlorine, condensing as metal a major portion of the vapors, collecting an additional portion as a fume product containing the major portion of the chlorine, recovering zinc values from said fume product by treatment with an oxide and mixing the chlorine with fresh crude material and reduction fuel for a subseguent volatilizing operation.

2. method of recovering metal values from crude zinc-bearing material which comprises volatilizing the'metal content of such material in the presence of chlorine, condensing as metal a major portion of the vapors, collecting an additional portion as a fume product containing the major portion of the chlorine, leaching the fume product, treating the wash water with an oxide to precipitate the zinc values and-mixing the remaining chloride with fresh crude material and reduction fuel' for subsequent volatilizing operation.

3-. A method of recovering metal values from crude zinc-bearing material which comprises volatilizing the metal content of such material in the presence of chlorine, condensing as metal a major portion of the vapors, collecting an additional portion as a fume product containing the majorportion of the chlorine, leaching the fume product,--

treating the wash water with lime and mix,

ing the resultant solution of calcium chloride with fresh crude material and reduction fuel for a subsequentvolatilizing operation. 4. A method of recovering metal values from crude zinc-bearing material which comprises volatilizing the metal content of such material in the presence of chlorine,

' condensing as metal'amajor portion'of the vapors, collecting an additional portion as a fume product containing the major portion of the chlorine and recovering the zinc values occurring as chloride in said fume by treatment with an oxide.

5. A method of recovering metal values from crude zinc-bearing material which comprises volatilizing the metal content of such material in the presence of chlorine, condensing as metal a major portion of the vapors, collecting an additional portion as a fume product containing the major portion of the' chlorine, leaching the fume, treating the wash water with zinc such material in the presence of a fluxing salt, condensing. as metal a major portion of the vapors, collecting an additional proportion as a fume'product containing the radical of said salt. and recovering the zinc values which are combined with said radical by treatment with an oxide.

7 That method of recovering metal values from crude zinc-bearing material utilizmg a retort furnace and condenser which comprises charging the retort with a mixture of said material and reduction fuel together with a small quantity of chlorine-bearing material in amount materially in excess of the capacity of the condenser whereby a substantial proportion of the metal values vaporized is discharged in the form of vapor from the condenser mouth, collecting said discharged vapor by deposit as a fume product containing at least a considerable proportion of the chlorine and recovering the zinc values which are combined with chlorine in said fume by treatment with an oxide.

8. That method of recovering metal values from crude zinc-bearing material-utilizing a retort furnace and condenser which comthe capacity of the condenser whereby a ues substantial proportion of the metal va vaporized is discharged in the form of vapor from the condenser mouth,- collecting said discharged vapor by deposit as a fume prod; not containing at least a considerable .por-

portion of the chlorine, leaching said fume and treati'ng'the wash water with an oxide to recover zinc values therefrom.

9. That method of recovering metal values from crude zinc-bearing material utilizing a retort furnace and condenserwhich comprises chargingfthe retort with a mixture of said material and reduction fuel together with a small quantity of chlorine-bearing -material' in amount materially in excess of the capacity of the condenser whereby a substantial'proportion of the metal values vaporiz ed is-dlscharged in the form of vapor from the condenser mouth, collecting said discharged vapor by deposit as a fume product containing atleast a considerable pro-.

portion of, the chlorine, leaching the fume,

precipitating the zinc values from the wash water by a reagent, and mixing the remaining liquid carrying the chlorine with fresh crude material and reduction fuel to provide acharge for a subsequent volatilizing operation.

10. That method of recovering metal values from crude zinc-bearing material utilizing a retort furnace and condenser which comprises charging the retort with a mixture of said material and reduction "fuel in amount materially in excess of the capacity of the condenser whereby a substantial proportion of the metal values vaporized is discharged in' the form of vapor from the condenser month, said mixture also including a quantity of a fiuxing compoundhaving a radical forming a soluble salt with zinc, collecting said discharge vapor by deposit as a fume containing at least a conhaving a radical forming a soluble salt with zinc, collecting said discharged vapor by.

deposit as a fume containing at least a considerable proportion of the radical, leachmg the fume, precipitating the zinc with a reagent and mixing the remaining liquid with fresh crude material and reduction fuel to provide a charge for a subsequent volatilizing operation.

12. That method of recovering metal values from crude zinc-bearing material utilizing a retort furnace and condenser which comprises charging the retort with a mixture of said material and reduction fuel in amount materially in excess of the capacity of the condenser whereby a substantial proportion of the metal values vaporized is discharged in the form of vapor from the condenser month, said mixture also including a quantity of fluxingdia'loid, collect ing said discharged vapor y deposit as a "fume containing a considerable proportion of the haIOgem-leaching the fume and precipitating the zinc from the wash water.

13. That method of recovering metal values from crude zinc-bearing" material utilizing a retort furnace and condenser which comprises char ing the retort with a mixture of said material and reduction fuel in amount materially in excess of the capacity of the condenser whereby a substantial proportion of the metal values vaporized is discharged in the form of vapor from the condenser month, said mixture also including a quantity of fiuxing haloid, collecting said discharged vapor by deposit as a fume 'containing'a considerable proportion of the halogen, leaching the fume, precipitating he zinc from the wash water and mixing the remaining haloid-bearing liquid with fresh crude material and reduction fuel to provide a charge for a subsequent volatilizing operation. i

In testimony whereof, I have signed my name to this specification.

. WILLIAM A. OGG. 

